The present invention relates to the field of manufacturing equipment for manufacturing liquid crystal display devices containing semiconductor integrated circuits and more particularly to apparatus and associated method for protecting semiconductor devices from damage due to static electricity.
Recent advances in electronic technology have resulted in accelerating miniaturization and higher resolution in all types of electronic appliances and components. In addition, light weight, portable information handling equipment such as mobile phones and laptop PCs are rapidly gaining in popularity in response to the increasingly information-based nature of the economy. Naturally, miniaturization and higher resolution also result in advances in display devices such as liquid crystal display devices, which are used extensively as displays for mobile devices, and the semiconductor integrated circuits which act as driving circuits for liquid crystal display devices.
The miniaturized circuits created by ever finer configuration of semiconductor integrated circuits are extremely fragile, and are increasingly likely to be damaged by static electricity built up during their manufacturing process and subsequent handling. Accordingly, there is an urgent need to develop anti-electrostatic measures to protect electronic devices containing semiconductor integrated circuits, including liquid crystal display devices.
A wide range of measures is already in place to prevent electrostatic damage to electronic devices containing semiconductor integrated circuits during their manufacturing process. One is to dispose a highly conductive metal on the surface of the manufacturing equipment and to use it to provide grounding. To prevent electrostatic charge from accumulating on factory operators, they normally wear an anti-static wristband which is always grounded, and manufacturing jigs and tools are made of materials which minimize the accumulation of electrostatic charge.
FIG. 3 shows a part of the conventional configuration of manufacturing equipment for liquid crystal display devices containing semiconductor integrated circuits. A liquid crystal panel 2, in which a semiconductor integrated circuit for driving the liquid crystal panel 4 is disposed on its wiring pattern terminal 3, is placed on the top working surface of the manufacturing equipment body 1. A discharge current limiting protective resistance 5 is inserted between the manufacturing equipment body 1 and ground 6.
As shown in FIG. 3, any electrostatic charge generated at the wiring pattern terminal 3 of the liquid crystal panel 2 is instantaneously discharged to the metal face of the manufacturing equipment body 1 which is located under the wiring pattern terminal 3. This, usually, causes electrostatic damage to the semiconductor integrated circuit used for driving the liquid crystal panel 4. A circuit device damaged by an electrostatic discharge may still appear to operate properly by barely switching ON and OFF if it is part of a digital signal processing circuit. However, its reliability has decreased. If the damaged integrated circuit is part of an analog signal processing circuit, such as an operational amplifier for determining the contrast of the liquid crystal display, such damage may directly degrade the display quality, causing a defective product in many cases.
To prevent this type of defect, the manufacturing equipment body 1 according to the prior art is connected to ground 6 via a discharge current limiting protective resistance 5. This limits the current passing through the discharge path to the ground 6 from the wiring pattern terminal 3 through the metal working surface of the manufacturing equipment body 1, thus enabling the gradual discharge of electrostatic charge.
In the conventional manufacturing equipment for liquid crystal display devices, the flow of electric current from the manufacturing equipment to the ground may be limited, but the surface of the manufacturing equipment has high conductivity and is a relatively very large metal surface. Viewed from the wiring pattern terminal 3, the large metal surface area of the manufacturing equipment appears effectively as a ground plane as it allows the accumulated electrostatic charge to spread very easily and therefore act as if it were grounded. Accordingly, electrostatic charge accumulated on the wiring pattern terminal 3 during the actual manufacturing process of liquid crystal display devices may be substantially instantaneously discharged to the metal surface of the manufacturing equipment, even when a current limiting resistance is used to ground the equipment, causing a problem of electrostatic breakdown.
The present invention solves this problem and aims to offer circuit device manufacturing equipment which prevents electrostatic damage of devices typically containing a semiconductor integrated circuit subject to damage due to electrostatic charge accumulation and/or discharge.
According to this invention there is provided manufacturing equipment for use in manufacturing electronic devices comprising circuits subject to damage from electrostatic charges, the equipment comprising a grounded conductive surface in close proximity to said electronic devices, the improvement comprising a protective resistive (dielectric) layer over said conductive surface, said protective layer having a thickness d (xcexcm) and a surface resistance of about (55/d)2xc3x97(1xc3x97105 to 1xc3x97108) ohm/square said protective layer located at least between said electronic device when said electronic device is disposed on said equipment and said equipment.
The circuit device manufacturing equipment of the present invention has a protective resistance layer with thickness of d (xcexcm) and a surface resistance value of (55/d)2xc3x97(1xc3x97105 to 1xc3x97108) ohm/square, which is placed between a rear face of a wiring pattern terminal of the circuit device placed on the manufacturing equipment and a surface of the manufacturing equipment facing the above rear face of the wiring pattern terminal.
The invention may also be practiced by a method for manufacturing electronic components wherein damage due to electrostatic charges during mounting of an integrated electronic circuit comprising semiconductor components on an electronic device wherein the device is positioned on an electrically grounded conductive working surface of a manufacturing equipment is prevented. According to the present invention, damage is prevented by placing a protective resistive layer having a thickness d in xcexcm, and a surface resistance of about (55/d)2xc3x97(1xc3x97105 to 1xc3x97108) ohm/square between said electronic device and said conductive working surface.
Provision of the protective resistance layer prevents easy spread of static electricity on the surface of the manufacturing equipment, and also prevents the surface of manufacturing equipment to have the state of as if it were grounded. As a result, a discharge current from the circuit device to the surface of manufacturing equipment may be limited during the manufacture of circuit devices, enabling the prevention of an electrostatic breakdown of circuit devices.